Question & Answer
Question
Receiving VTAM message IST154I EXPANSION FAILED FOR IO BUFFER POOL
Answer
VTAM IO buffers are allocated out of MVS CSA storage. You can limit the amount of total CSA used by VTAM with the CSALIMIT VTAM START option. The IST154I message indicates that the VTAM IO Buffer pool was trying to expand to get more IO buffers to satisfy a demand, but could not get CSA storage due to the VTAM CSALIMIT being reached.
The CSALIMIT is a user defined parameter and must be evaluated from time to time to ensure it is not set too low which will prevent VTAM processes such as buffer expansion, etc. CSALIMIT must be set high enough to allow for CSA needs during network recovery, etc. You can display the value of the CSALIMIT with the VTAM Display BFRUSE command. You can also change the value on the fly with the MODIFY VTAMOPTS command or the MODIFY CSALIMIT command while VTAM is running. If you feel you have CSALIMIT set high enough and still getting the IST154I message,
issue the VTAM MODIFY CSDUMP command to get a dump of VTAM and contact IBM z/OS Comm Server support for diagnostic assistance.
Product Synonym
ZOSCS COMMSERVER
Was this topic helpful?
Document Information
Modified date:
04 June 2015
UID
dwa1194880